Background: It is well established that several cardiovascular risk factors exhibit strong tracking from early childhood into adult life and an increasing body of evidence supports that cardiovascular diseases (CVD) have origins in the foetal or neonatal environment. Studies in both humans and experimental animals have suggested that changes in the peri- and early post-natal intake of n-3 polyunsaturated acids can affect the development of CVD risk factors in adult life. This leads to the hypothesis that n-3 fatty acid supplementation in the latter half of normal pregnancy will have a beneficial impact on offspring CVD risk, which would have important potential implications for our understanding of the pathogenesis of CVD and their prevention. Specific aims: The aims of the present study is to investigate effect of supplementation with 2.7 grams long chain n-3 fatty acids per day during third trimester of uncomplicated pregnancies on blood pressure, autonomic function, and glucose and lipid metabolism in the 17 year old offspring. Research design and methods: The study is based on long term follow-up of a randomised controlled trial from 1990, in which 533 pregnant women were randomised to long chain n-3 fatty acids (2.7 grams per day), placebo with olive oil (4 grams per day) or no oil. This is the largest and oldest trial cohort worldwide of its kind, and follow-up will be facilitated by the fact that most offspring still live in the same area as they were born and by unique opportunities for registry linkages in Denmark. Briefly, all children will be invited in writing and those accepting to participate will be given a standard physical examination including blood sampling and measuring of mean arterial blood pressure, waist circumference, BMI and heart rate variability. A subgroup of children comprising the off-spring from women categorized as having a low basic fish-intake (approx. 100 individuals) will undergo additional examination including 24 hour heart rate variability. Long term objectives: The present study should be regarded as a pilot study preceding a more in depth elucidation of possible underlying mechanisms. Given that fish oil supplementation during pregnancy has positive effects on offspring CVD risk, it would be important to further explore the possible underlying mechanisms. If the data support the overall hypothesis that foetal exposure to long chain n-3 fatty acids has long term effects on CVD risk factors, this might lead to a relatively cheap and easily implemented strategy for the prevention of CVD in the future. PUBLIC HEALTH RELEVANCE: If our data confirm a relationship between maternal fish oil consumption during pregnancy and decreased development of cardiovascular disease risk factors in the young offspring, than this would imply an enormous potential for disease prevention. That is both because pregnant women as a group may be more attentive to lifestyle recommendations, but also because of the relatively limited time period of the intervention.